The invention relates to an air heater, and seeks to provide a simple heater arrangement which can accommodate substantial variations in the air inlet temperature.
Known air heaters operate on a straightforward heat exchange principle; a hot fluid, normal gas such as combustion gases from a burner gives up heat to the air as it flows through the heater. A typical heat exchanger employs heat pipes to effect the transfer of heat from an hot fluid duct to the air duct. While this arrangement is generally satisfactory, when the air inlet temperature falls, so does the efficiency of the heat exchanger which is adversely affected, resulting in a disproportionately lowered outlet temperature. This can produce problems in the installation to which the heated air is to be fed.